By Brenda Goh

SHANGHAI (Reuters) - China's table tennis team travel to Rio de Janeiro under a cloud of controversy as fans lament that even being the world champion does not guarantee a coveted Olympic singles spot in one of the world's most competitive sporting teams.

The failure of world number one Liu Shiwen to clinch one of China's two spots in the competition was greeted with an outcry at home described by local news outlet Sina Sports as "one of the most tragic things to happen to the Chinese women's team in the last 20 years".

The tough selection - which fell to defending London champion Li Xiaoxia and world number two Ding Ning - also underlines how China is likely to once again dominate the medal tables at Rio as it did in the 2008 and 2012 Olympics.

"That's a crazy story in itself that the world's best ranked player won't be playing in the singles event, but that just shows the strength of the Chinese team," Matthew Pound, from the sport's governing body, the International Table Tennis Federation, told Reuters.

In a handwritten letter published by a journalist from state broadcaster CCTV in May, 25-year-old Liu, who will play in the team event instead, did not directly address the decision, but said "all our efforts and preparations are for that moment when the red, five star flag is raised up high."

Chinese table tennis players currently make up the majority of the world's top five ranked men and women. The country won all four medals in the 2008 Beijing Olympics and repeated the feat at the 2012 London Olympics.

In the men's singles, China will be represented by London champion and world number four Zhang Jike and world number one Ma Long, while Fan Zhendong and Xu Xin -- number two and three respectively -- will participate in the team events.

Germany, North Korea, Japan and South Korea are expected to put up the hardest fights for medals at the Riocentro venue, where the matches will run throughout the Games from Aug. 5-21.

The youngest player to take the stage will be 15-year-old Adrian Diaz, who will be Puerto Rico's first Olympic table tennis player, while the oldest is 54-year-old Chinese-born Spanish player He Zhiwen.

Paralympians Natalia Partyka of Poland and Australia's Melissa Tapper are notable participants, while surprises could come from Britain, whose men's team broke a 33-year-long medal drought in March with a bronze at the world team championships.

(Reporting by Brenda Goh; Editing by Ken Ferris)